Neurogenic hypertension in the Guillain-Barré syndrome

Biochemical Assessment of Pheochromocytoma and Paraganglioma

Pheochromocytoma and paraganglioma (PPGL) require prompt consideration and efficient diagnosis and treatment to minimize associated morbidity and mortality. Once considered, appropriate biochemical testing is key to diagnosis. Advances in understanding catecholamine metabolism have clarified why measurements of the O-methylated catecholamine metabolites rather than the catecholamines themselves are important for effective diagnosis. These metabolites, normetanephrine and metanephrine, produced respectively from norepinephrine and epinephrine, can be measured in plasma or urine, with choice according to available methods or presentation of patients. For patients with signs and symptoms of catecholamine excess, either test will invariably establish the diagnosis, whereas the plasma test provides higher sensitivity than urinary metanephrines for patients screened due to an incidentaloma or genetic predisposition, particularly for small tumors or in patients with an asymptomatic presentation. Additional measurements of plasma methoxytyramine can be important for some tumors, such as paragangliomas, and for surveillance of patients at risk of metastatic disease. Avoidance of false-positive test results is best achieved by plasma measurements with appropriate reference intervals and preanalytical precautions, including sampling blood in the fully supine position. Follow-up of positive results, including optimization of preanalytics for repeat tests or whether to proceed directly to anatomic imaging or confirmatory clonidine tests, depends on the test results, which can also suggest likely size, adrenal vs extra-adrenal location, underlying biology, or even metastatic involvement of a suspected tumor. Modern biochemical testing now makes diagnosis of PPGL relatively simple. Integration of artificial intelligence into the process should make it possible to fine-tune these advances.

Autonomic involvement in Guillain-Barré syndrome: an update

BACKGROUND

Guillain-Barré syndrome (GBS), an inflammatory, usually demyelinating polyradiculopathy, is characterized by ascending symmetrical limb weakness, sensory disturbances, and absent or reduced deep tendon reflexes. There is extensive literature suggesting that GBS is associated with autonomic dysfunction in up to two-thirds of patients. However, it is interesting that there is still no consensus amongst medical professionals regarding whether GBS patients should be routinely screened for autonomic nervous system (ANS) neuropathy. This is an important issue, as the mortality rate from presumed ANS abnormalities now exceeds that of respiratory failure. Given the long interval since this literature was last comprehensively reviewed, an update on this topic is warranted.

METHODS

A PubMed search yielded 193 results with the terms "GBS or Guillain-Barré syndrome and autonomic symptoms" and 127 results with the terms "GBS or Guillain-Barré syndrome and dysautonomia."

RESULTS

This review will summarize the current literature involving GBS and autonomic dysfunction in terms of presentation, management, and a brief discussion of prognosis. We also examine prospective approaches that may be helpful and update a proposed management plan.

Rapid determination of catecholamines in urine samples by nonaqueous microchip electrophoresis with LIF detection

A method was developed for the rapid separation of catecholamines by nonaqueous microchip electrophoresis (NAMCE) with LIF detection, A homemade pump-free negative pressure sampling device was used for rapid bias-free sampling in NAMCE, the injection time was 0.5 s and the electrophoresis separation conditions were optimized. Under the optimized conditions, the samples were separated completely in <1 min. The average migration times of the epinephrine (E), dopamine (DA), and norepinephrine (NE) were 34.26, 43.81, and 50.07 s, with an RSD of 1.05, 1.26, and 0.89% (n = 7), respectively. The linearity of the method ranged from 0.0125 to 2.0 mg/L for E and 0.025~4.0 mg/L for DA and NE, with correlation coefficients ranging between 0.9978 and 0.9986. The detection limits of E, DA, and NE were 2.5, 5.0, and 5.0 μg/L, respectively. The recoveries of E, DA, and NE in spiked urine samples were between 86 and 103%, with RSDs of 4.5~6.8% (n = 5). The proposed NAMCE with LIF detection combined with a pump-free negative pressure sampling device is a simple, inexpensive, energy efficient, miniaturized system that can be successfully applied for the determination of catecholamines in urine samples.

Simultaneous determination of catecholamines and amino acids by micellar electrokinetic chromatography with laser-induced fluorescence detection

A selective and sensitive method was developed for separation and simultaneous determination of catecholamines and amino acids by MEKC with LIF. Interestingly enough, such work has been firstly performed on catecholamines derivatized with 4-chloro-7-nitro-2,1,3-benzoxadiazole and the detailed derivatization mechanism was discussed. After derivatization at 60 degrees C for 20 min, NBD-labeled catecholamines and amino acids were separated in a buffer system containing 10 mM sodium tetraborate-Na2HPO4, 20 mM SDS, and 10% v/v ACN at pH 9.75. SDS micelles were employed to improve the fluorescence intensity of catecholamine derivatives efficiently. Under optimum conditions, two catecholamines and 11 amino acids were separated in a short 13 min analysis time and the RSDs for migration time and peak area were less than 0.60 and 6.50%, respectively. The method was successfully applied for the quantification of catecholamines and amino acids in Portulaca oleracea L., human urine sample, and mixed injection sample.

Determination of catecholamines in pheochromocytoma cell (PC-12) culture medium by microdialysis-microbore liquid chromatography

An in vitro microdialysis system was constructed for the measurement of catecholamines in pheochromocytoma cell culture medium. The novel microdialysis device is composed of a petri dish, a dialysis membrane and two transmission tubes. The dialysis membrane is located in the space of a petri dish such that it is immersed in the culture medium. Catecholamines contained in the culture medium diffused into a designed dialysis membrane with sufficient recovery (about 60%). Dialysates were collected by a sampling loop and introduced by an on-line injector to a microbore liquid chromatographic system for analysis of catecholamines. This assay yielded a detection limit of 0.2-0.5 pg/injection with acceptable intra- and inter-assay reproducibilities in 5 microl of dialysates. To evaluate the on-line microdialysis system, PC-12 cells were cultured in a petri dish within an incubator. The baseline concentration of dopamine in PC-12 cell culture medium was about 0.29 ng/ml which was elevated to 2.43 ng/ml after treatment with 0.5 mM potassium cyanide. In conclusion, the present microassay provides for the sensitive, direct measurement of catecholamines in culture medium while minimizing pretreatment procedures for sample preparation.

Monitoring of blood catecholamines by microdialysis and microbore LC with a dual amperometric detector

The accuracy of in vivo microdialysis for monitoring blood catecholamines and their metabolites in Lan-Yu mini-pigs was evaluated. To prevent blood clots and irritation, a microdialysis probe was secured in a Y-shaped tube. The tube was connected to an arterio-venous shunt, in a mini-pig, for in vivo experiments. Perfusates were injected onto a microbore LC equipped with a dual electrochemical detector (the upstream electrode was set at an oxidizing potential and the downstream electrode was set at a reducing potential. The typical large offscale peak or interfering peaks on the anodic chromatograms were mostly eliminated on the cathodic chromatograms, thereby providing reliable measurements of early eluters. Early eluates, such as norepinephrine and epinephrine, with reversible redox behaviour could be detected at the downstream reducing electrode. A comparison of the present method and a conventional blood-drawing method showed good correlation (r = 0.775-0.983 for all analytes).

Autonomic dysfunction as the presenting feature of Guillain-Barré syndrome

Autonomic dysfunction has been demonstrated in various conditions associated with peripheral neuropathy such as acute intermittent porphyria, amyloidosis, and Guillain-Barré syndrome (GBS). In the latter, hypertension is an associated complication that typically occurs after neurological signs are already present. We report a case of a patient with autonomic dysfunction as the presenting feature who was admitted to the coronary unit with chest pain and hypertension. Subsequently, he developed progressive symmetric muscle, weakness, sensory changes, and areflexia. GBS was then diagnosed based on the clinical picture, albuminocytologic dissociation in the cerebrospinal fluid, and electrodiagnostic abnormalities suggestive of demyelinative polyneuropathy with conduction block. Few cases in the literature have reported autonomic dysfunction as the presenting feature of GBS, such as in this case. In a previously asymptomatic patient, acute onset of autonomic dysfunction should alert the physician to the possibility of an acute polyneuropathy, such as GBS.

A case of Guillain-Barré syndrome accompanied by sympathetic overactivity and hypertensive encephalopathy

Hypertension has often been observed in patients with Guillain-Barré syndrome, and various underlying mechanisms have been implicated. We report the case of a child with the Guillain-Barré syndrome whose hypertension was associated with increases in both renin activity and circulating catecholamines. This case also appeared to be complicated by hypertensive encephalopathy. Following administration of intravenous regitine, a blood pressure change was observed and cardiac performance was assessed by two-dimensional echocardiography. Results indicated that increased total peripheral resistance may have been responsible for the symptoms and the hypertension. The hypertension was effectively managed by nifedipine, captopril and prazosin without the need for beta-blockade.

The mechanism responsible for hypertension in a patient with Guillain-Barré syndrome

We report a case of hypertension associated with Guillain-Barré syndrome. In this case, the circadian variation of blood pressure was interrupted. Examination of neurohumoral factors revealed a hyperactive sympathetic nervous system and an increase in plasma renin activity. Clonidine, which acts centrally to inhibit sympathetic outflow, did not suppress serum norepinephrine or epinephrine. These observations suggest that autonomous hyperactivity of the efferent pathway of the sympathetic nervous system may cause the sustained hypertension throughout the day in this case.

Autonomic involvement in Guillain-Barré syndrome: a review

Autonomic neuropathy is an important and common complication of Guillain-Barré syndrome (GBS). Manifestations be present in cardiovascular, sudomotor, gastrointestinal and other systems involving both sympathetic and parasympathetic fibers. Some apparently selective acute autonomic neuropathies may be subvarieties of GBS. Experimental work in animal models, pathological studies of GBS patients, and autonomic function studies have provided some help in the understanding of this complication. In managing GBS patients with autonomic dysfunction there are important practical considerations that can improve their care. In this article we review the literature on autonomic neuropathy in GBS and propose a management scheme to accommodate it in the overall treatment of the neuropathy.

Simultaneous measurement of serotonin, catecholamines and their metabolites in mouse brain homogenates by high-performance liquid chromatography with a microbore column and dual electrochemical detection

A dual electrochemical detector with two working electrodes (anode and cathode) suitable for high-performance liquid chromatography with a microbore octadecylsilica column was applied for the simultaneous measurement of norepinephrine, epinephrine, dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, 5-hydroxyindoleacetic acid, 3-methoxytyramine and 5-hydroxytryptamine (serotonin) in mouse brain homogenates. Microbore high-performance liquid chromatography provides very good resolution of these analytes and offers selective detection of biogenic amines and their metabolites on the basis of their retention behaviour and electrochemical reversibility. The large early-eluting peak of brain homogenates was eliminated on cathodic detection, thereby providing reliable measurements of early eluates. The detection limit of this method was ca. 0.2-0.5 pg per injection for all components, at a signal-to-noise ratio of 3. Owing to the high sensitivity, the brain tissue samples could be kept very small (less than 10 mg). Isocratic separation of these analytes was achieved within 15 min; hence over 90 analyses could be performed in a single working day. This simple, efficient and sensitive method can be used as a basic research tool for the assaying of biogenic amines and their metabolites in brain homogenates.

Simultaneous measurement of serotonin, catecholamines and their metabolites in cat and human plasma by in vitro microdialysis-microbore high-performance liquid chromatography with amperometric detection

A method for the simultaneous measurement of norepinephrine, epinephrine, dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, serotonin and 5-hydroxyindole-3-acetic acid in cat and human plasma by in vitro microdialysis-microbore high-performance liquid chromatography with electrochemical detection is described. The detection limit (signal-to-noise ratio = 3) is about 0.05-0.1 pg per injection. The volume of plasma samples required is very small (< 200 microliters), hence there is minimal blood loss in repeated blood sampling, especially in experiments using small animals. Within 15 min, a fast isocratic separation of these analytes by using a microbore reversed-phase ODS column is achieved, hence over 90 analyses can be performed in a single working day. As microdialysis per se is not destructive to plasma samples, the remaining plasma sample and perfusate can be repeatedly analysed for other substances. This simple, efficient and sensitive method can therefore be used as a routine clinical and basic research technique in the investigation of blood biogenic amines and their metabolites.

Involvement of brain stem noradrenergic neurons in the development of hypertension in spontaneously hypertensive rats

This study attempted to investigate the possible involvement of the brain stem noradrenergic system in the development of hypertension in spontaneously hypertensive rats. Steady-state norepinephrine, dopamine, serotonin and 5-hydroxyindoleacetic acid concentrations and norepinephrine turnover were determined in the individual brain stem nuclei using high performance liquid chromatography with electrochemical detection. Decreased norepinephrine contents in the nucleus tractus solitarii in spontaneously hypertensive rats compared with Wistar-Kyoto rats at the age of 4, 8, and 16 weeks were demonstrated. In later stages (8 and 16 weeks), increased norepinephrine levels were observed in the nucleus reticularis gigantocellularis, the A1 and A5 areas. Norepinephrine turnover was not different between spontaneously hypertensive rats and Wistar-Kyoto rats in the nucleus tractus solitarii at the age of 4 and 16 weeks and increased in the nucleus reticularis gigantocellularis of spontaneously hypertensive rats at 16 weeks. Our results indicate that altered norepinephrine metabolism in the specific brain stem nuclei, especially the consistently decreased norepinephrine in the nucleus tractus solitarii of spontaneously hypertensive rats, contribute to the development of genetic hypertension.

Catecholamines and their metabolites

The research on biosynthesis, physiology, pharmacology, regulation and degradation of catecholamines has continuously increased for more than 50 years. This is not unexpected because of the fact that catecholamines are involved in so many life processes such as nerve conduction, blood circulation and hormone regulations in health and disease. This demands that methods for their determination should be improved, and in fact during the years a number of analytical methods have been published. About 20 years ago radioenzyme techniques with thin-layer chromatographic (TLC) separation of radiolabelled catecholamine derivatives were developed which greatly contributed to our knowledge of physiological concentrations of catecholamines in biological media, particularly in plasma and brain. Radioimmune methods were successful for analysis of a number of analytes, but for catecholamines radioimmunoassays developed slowly. We believe that the greatest potential for radioimmunochemical methods lies in their ability to localize catecholamines and metabolites at the cellular and subcellular levels. With the advent of gas chromatographic-mass spectrometric (GC-MS) and high-performance liquid chromatographic (HPLC) procedures analysis of catecholamines improved greatly., The equipment for GC-MS is expensive and requires technical skillfulness, but in experienced hands a lot of new biological data have emerged. An outstanding quality with GC-MS is that the method offers the ability to identify unknown compounds and is relatively free from interferences from extraneous compounds. In comparison with GC-MS, HPLC is versatile and has gained a widespread use. Applications for research in the catecholamine field are numerous. In general, the sensitivity and specificity are satisfactory with HPLC, but it should be borne in mind that a number of pitfalls can obscure the results. This involves both sample handling, clean-up and chromatographic procedures. At present, HPLC is the most expanding field in chromatographic determination of catecholamines and their metabolites. This is particularly the case for HPLC with electrochemical detection which has revolutionized our analytical potential in this field. These chromatographic procedures continue to develop. The prerequisites for further improved methods such as capillary zone electrophoresis and combined HPLC-MS are at hand and hopefully will soon come into more general use for analysis of catecholamines in biological samples.